Since network resource of mobile ad hoc network (MANET) is limited due to the contention-based wireless communication channel at the medium access layer and energy of mobile nodes is constrained due to the energy-limited batteries, the scalability issue is one of main research topics in developing MANET routing algorithms. Therefore, this paper analyzes the message complexities of group shared tree (GST) and source-specific tree (SST) that are implemented in most MANET multicast routing algorithms. Simulation demonstrates that in a wireless ad hoc network where SST and GST are well maintained during the simulation, SST algorithm is able to achieve very competitive performance (i:e: less message complexity) under the multiple packet transmissions, in comparison with GST where no core selection algorithm is adopted.